Hey everyone _ I was wondering if someone can tell me why the following code runs fine without errors when calling

flow.run()

but

flow.register()

flags an error mainly the healthcheck throws this error - which I see referenced in the documentation … I am using prefect

v0.11.4

ValueError: Mapped tasks with custom result locations must include
{filename} as a template in their location.

Please see the code below

import os
from prefect import task, Flow
from prefect.engine.results import S3Result


@task
def gen_list():
    return [x for x in range(10)]


@task
def add(x, y):
    return x + y


@task
def multiply(x, y):
    return x * y


result = S3Result(
    bucket=os.environ["AWS_BUCKET"],
    location='prefect-testing/{task_name}/{map_index}.prefect'
)

with Flow('Test Flow', result=result) as flow:
    x = gen_list()
    y = gen_list()
    added = add.map(x, y)
    multiplied = multiply.map(added, added)

# flow runs fine if running locally
flow.run()


"""
flow fails to register
ValueError: Mapped tasks with custom result locations must include
{filename} as a template in their location.
"""
flow.register('Test Project')

Hi @Marwan Sarieddine! As the error message mentions, you need to include

{filename}

in the location template for your result. So in this case you'd have something like:

# ...imports and tasks

result = S3Result(
  bucket=os.environ["AWS_BUCKET"],
  location="prefect-testing/{task_name}/{file_name}_{map_index}.prefect"
)

# ...

Hi @nicholas - yes I understand that I need to update the template to include

{filename}

- but what I don’t understand is why

{filename}

is necessary if flow.run() locally doesn’t throw errors and works fine ?

It looks like there's an open issue that touches this and explains why the filename isn't throwing an error locally (it isn't populated); you might add your code to that as well 🙂

I see - thanks ! I suppose the answer is here “I don’t think we populate the 

filename

 attribute for local runs”

Thanks @Marwan Sarieddine!

sure - thank you!